Resin additives such as phenolic antioxidants, UV absorbers and hindered amine compounds are known to suppress degradation of organic materials such as synthetic resins by light or heat.
As the compounds used as such resin additives, those compounds which generally have a high melting point and are not likely to plasticize a resin or vaporize from a resin, such as tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyloxymethyl)methane and tris(2,4-di-tert-butylphenyl)phosphite, are preferred. However, when such a compound is made to have an excessively high molecular weight, the additive cannot move within the resin, so that the stabilizing effect thereof tends to be decreased.
Meanwhile, low-melting compounds such as stearyl(3,5-di-tert-butyl-4-hydroxyphenyl)propionate and bis(2,2,6,6-tetramethylpiperidyl)sebacate have a relatively low molecular weight and have excellent initial stabilizing effect; however, since they easily vaporize from a resin, their long-term stabilizing effect is poor. Furthermore, since, for example, these low-melting compounds are liquid, viscous or powdery and form large aggregates due to caking during storage, the ease of handling is poor and, therefore, they are required to be masterbatched in order to improve the ease of handling.
However, when used in a crystalline resin, those compounds usually used as a resin additive have a low compatibility with the resin and, in the preparation of a masterbatch containing such a compound at a high concentration, there is a problem that the additive compound exudes to the surface of the masterbatch pellet to cause caking of the pellet. Therefore, such an additive compound can be blended in an amount of only 50 parts by mass or so with respect to 100 parts by mass of a crystalline resin, so that the merits of making the additive compound into a masterbatch are small.
Particularly, although hindered amine compounds obtained by a reaction between a piperidinol and a fatty acid exhibit excellent antiweatherability-imparting effect, they are likely to assume a liquid form at a low molecular weight and, in cases where they are made into a masterbatch in order to improve the ease of handling, since the additive exudes to the surface of the masterbatched resin composition and shows adhesiveness, it is required that the masterbatch have a low concentration. Furthermore, in cases where the concentration of such hindered amine compound is high, there is also a problem that the strand strength during masterbatch production becomes low, so that a masterbatch cannot be stably and continuously produced.
As a method of improving the ease of handling and the like of an additive, there have been proposed, for example, a method in which the tackiness is suppressed by masterbatching an additive compound with an oil-absorbing polymer (Patent Document 1), a method in which strand breakage is inhibited by making an additive compound into a masterbatch having a core layer and a sheath layer (Patent Document 2), a method in which the tackiness is suppressed and strand breakage is inhibited by masterbatching an additive compound with an organic acid metal salt (Patent Document 3), a method in which an additive compound is made into a microcapsule (Patent Document 4) and a method in which the powder characteristics are improved by promoting crystallization of a low-melting flame retardant (Patent Document 5). All of these are techniques that improve the ease of handling of a liquid low-melting additive.